Anodes and cover of electrolytic cells



March 26, 1957 c. B. BROWN 2,786,810

' ANODES AND COVER OF ELECTROLYTIC CELLS File c l Sept. 9, 1952 3Sheets-Sheet 1 IHVEHTOL- March 26, 1957 c B. BROWN 2,786,810

ANODES AND COVER OF ELECTROLYTIC CELLS Filed Sept. 9, 1952 3Sheets-Sheet 2 *TLTJELHSE March 1957 Filed Sept. 9; 19.52

PIC-l5.

c. 5. BROWN 2,786,810

ANODES AND COVER OF ELECTROLYTIC CELLS 3 Sheets-Sheet 5diliiiiiiiiiiiilin A"/ I IIIIIIIII/Iillll/ United States Patent ANODESAND COVER OF ELECTROLYTIC CELLS Collingwood Bruce Brown, Montreal,Quebec, Canada, assignor to Dominion Tar and Chemical Company, Montreal,Quebec, Canada, a corporation of Canada Application September 9, 1952,Serial No. 308,682

3 Claims. (Cl. 204219) This invention relates to an electrolytic cellfor the manufacture of chlorine and in particular to an electrolyticcell having a flowing mercury cathode.

, Two types of electrolytic cells having mercury cathodes are incommercial operation at the present time. These are primarily devoted.to the electrolysis of brine to produce chlorine, caustic soda and/orother sodium compounds. The particular type of electrolytic cell withwhich my invention is concerned is one which has a flowing mercurycathode of which there are several commercial variations known as theKrebs cell, the De Nora cell, the Mathieson cell, etc. These cellsconsist of two parts: a primary cell in which the brine is electrolysedto produce chlorine and sodium amalgam, and a secondary cell in whichthe amlgam is decomposed with water to produce aqueous caustic sodasolution, hydrogen and mercury. My invention is concerned with thestructure and operation of the primary cell.

The primary cell in which the brine is electrolysed is a trough having aU-shapcd cross section and inclined in a longitudinal direction toprovide for the necessary flow of mercury and brine. Such troughs aremade of some suitably resistant material. For example, some are made ofconcrete, others of steel lined with rubber or ceramic tile. Provisionis made, usually, in the bottom of the trough, for an electricalconnection to the flowing mercury cathode.

The anode assembly of such cells consists of graphite blocks suspendedfrom the cover or top of the cell by means of stems, also made ofgraphite. These anodes arearranged in rows across the primary cell withthe longitudinal axis of the block parallel to the longitudinal axis ofthe primary cell. The electrical connections to the anodes are made bymeans of clamps around the part of the stem which protrudes above thecover. The escape of the chlorine through the pores of the graphitestemsis prevented by impregnating them with some suitable material.

The cover to the cell, which is made of some suitable corrosionresistant material, in addition to serving as a holder for the anodesalso serves as the chlorine collector. Usually this cover is mounted onthe trough, i. e., bottom part of the primary cell, in such a mannerthat it can be raised orlowered and so permit adjustment of the gapbetween the anode and cathode (called the electrolysis gap) to anydesired dimension.

These electrolytic cells are operated in the following manner. Brineusually enters the primary cell at the higher end and flows beneath,around and over the anode blocks toward the lower end, co-currently withthe mercury, leaving a space beneath the cover for the collection ofchlorine. When a voltage drop is applied across the cell between thegraphite anode and the mercury cathode, chlorine and sodium amalgam areproduced. The chlorine rises to the top of the brine and is collectedbeneath the cover and eventually led away. The amalgam flows along thebottom of the primary cell to the secondary cell or decomposer where itis converted by means of water to sodium hydroxide solution, hydrogen,and mercury containing some residual amalgam which is returned to theprimary cell. The electrolysed brine leaves the lower end of the cell,is brought back to strength by the addition of salt, treated for removalof impurities, and recycled.

While cells of this type operate reasonably well they, nevertheless,have several disadvantages. For instance, one disadvantage is thatchlorine is evolved on the lower surface of the anode. This chlorinetends to form a layer of bubbles because the velocity of the brine inthe electrolysis gap is so low that the bubbles are not swept away. Thislayer of chlorine bubbles obstructs the passage of the current andrequires a higher voltage in order to get the required quantity ofcurrent to flow. That the presence of bubbles hinders the flow ofcurrent is demonstrated by the fact that the anode block wears most atthe outer edges probably due to greater flow of current (but possibly toa condition conductive to more rapid oxidation) and it is the outeredges from which the chlorine can escape most readily. Many attempts tofacilitate and provide for the removal of these bubbles. such as holesor slots in the anode, have been tried with partial though not completesuccess. The chief disadvantages of the use of slots or holes are that(l) the effective area of the anode is reduced and (2) the constructionof the anode is more costly.

Another disadvantage with anodes of the type used up to now is that ofobtaining a satisfactory mechanical and electrical connection betweenthe stem and the anode block. In order to keep the consumption ofelectric power as' low as possible, it is necessary to keep the voltagedrop across this connection as low as possible. The best methods used todate to achieve this involve eX- pensive machining operations, as forinstance in the De Nora'cell where the stem and block are threaded andscrewed together.

A voltage drop is also present in the stern itself and in the clampconnection at the top. At present such voltage drops are kept to aminimum by increasing the cross section of the stem and using highpressures and corrosion resistant materials for the clamp, etc. Butelectrical connections of this type are expensive and requireconsiderable labour to install and maintain.

. Still another disadvantage of the type of anode assembly which is usedtoday is that about half of the graphite is wasted. The anode blockultimately wears in a non-uniform manner to such a thickness that it canno longer be used safely or economically and must be discarded. The stemis usually used twice and then it is discarded.

Another disadvantage of the cells which are used today is that there isinsuflicient mixing of the brine, i. e., the brine in the electrolysisgap does not become mixed with that flowing above and around the blocks.As a consequence the brine concentration in the electrolysis gap mayoften reach undesirably low levels, particularly at the exit end of thecell.

Many of these disadvatages are overcome by my invention. This isachieved by placing graphite blocks parallel to each other with theirlongitudinal axes at right angles to the longitudinal axis of theprimary cell. These blocks extend from one side of the cell to the otherand are supported on two or more spacer strips extending along thebottom of the primary cell. The thickness of these strips provides therequired gap between the anode and the cathode. Between adjacent anodeblocks is a narrow space to permit the escape of chlorine. Over eachspace gap is a hood to collect the chlorine. The anodes, which arecoated on their upper surface with some suitable sealing material toprevent the escape of chlorine through the pores of the graphite,together with the hoods form the cover of the cell. The

anodes are so disposed in the primary cell that the brine is preventedfrom flowing above and around the anodes, but is caused to flow only inthe electrolysis gap, i. e., the gap between the anode and the cathode-As a conse quence the brine fiows through the electrolysis gap at a muchgreater velocity.

As the anode wears away .on its under surface, the electrolysis gap isadjusted by periodically removing the anode and machining the under sideso that it is once again a level smooth surface.

My invention can be more fully appreciated and understood by a study ofa particular embodiment. Such an embodiment is shown in the drawings;Fig. l is a plan of my new electrolytic cell; Fig. 2 is a section alongthe longitudinal axis; Fig. 3 is a section across the cell.

The primary cell consists of an elongated trough 1 having a flatU-shaped cross section made of steel, the walls of which are lined withrubber. This trough is gently inclined in a longitudinal direction. Atthe higher end of the primary cell is a mercury inlet 2 and a brineinlet 3; at the lower end is a brine outlet 4 and an amalgam outlet 5leading to the secondary cell 6. The graphite anodes 7 which some aspart of the cover of the primary cell 1 are placed in the cell parallelto each other with their longitudinal axes at right angles to thelongitudinal axis of :the primary cell. These anodes extend to each sideof the primary cell. Between adjacent anodes is a space 8 to permit theescape of chlorine from beneath the anode. Along each anode in a shallowgroove is a copper distributor cable 9 enclosed in lead It). This cableis attached by means of cable connectors 11 to the cell distributionbusbar 12. The spacers 8 between the anodes are covered throughout theirlength by hoods 13 which'are supported by the anodes 7. These hoods 13are connected individually by take-oils 14 to the chlorine collectorheader 15. The anodes 7 are sup ported on strips of hard rubber isrunning the full length of the cell. The strips 16 serve to support theanodes at the requisite distance from the mercury cathode 17. The space18 between the anode 7 and the cathode 17 is tilled wtih brine, thelevel of which in the cell is indicated by 19. The space between theends of the anodes 7, the hoods 13, and the wall of the cell are sealedwith putty as shown at 20. Similarly, the joints between the hoods l3and the anodes '7 are sealed with putty as shown at 21. Each graphiteanode 7 is grooved longitudinally along each side as shown at 22 toreceive the hood 13. The upper surface of the anodes is coated with asealing material 23 to prevent the escape of chlorine through theporesof the anodes.

The advantages of my invention are many.

1. The usual cover is eliminated thereby reducing capital andmaintenance costs.

2. The elimination of the stem and connections to the anode blockresults in a reduction in voltage loss and graphite consumption. Thecarbon consumption is reduced by having a greater proportion of thegraphite available for use in electrolysis. The voltage loss is reducedby eliminating one connection and shortening the path of the currentthrough the graphite.

3. With little or no increase in the quantity of brine from the cell andthe concentration of sodium in the mercury stream is more uniform.

6. The assembling and dismantling of this new primary cell can be moreeasily accomplished than is possible with present cells.

It is obvious that while the above is a preferred form of my invention,there are many variations which it could take without departing from thespirit of my invention.

For instance, the hoodsfor collecting the chlorine may have a variety ofshapes. In cross section they might have the shape of an inverted V orof a semi-circle. In addition if desired a single hood may be made tocover several of the spaces between the anodes. The chlorine hoods couldalso be made to cover one anode block only; be grouted, sealed orgasketed to that block; and sealed or gasketed to each other to containthe chlorine. Furthermore these hoods may be constructed of any one of avareity of corrosion resistant materials, such as, concrete, rubberlined steel, glass lined steel, etc. The chlorine collection hoods couldalso be eliminated by using a specially extruded and/ or machinedgraphite section as combined anode and hood.

The electrical connections need not take the precise form shown in theparticular description, but may be made in a variety of ways withoutdeparting from the spirit of my invention. For example, the electricalconnections might be made by means of prongs from a copper busb-arextending into holes in the graphite blocks or by clamping theconnections around a raised extruded portion.

It is also possible without departing from the spirit of my invention tohave the strips which support the anodes made of concrete or porcelainas an integral part of the primary cell.

The sealing material used on the upper surface of the anodes to preventthe escape of chlorine may be one of a variety of materials, such as,pitch, asphalt, rubber, wax, etc.

Having thus described my invention, I claim:

1. An electrolytic cell comprising an elongated trough of U-shaped crosssection, inclined in a longitudinal direction to provide for the flow ofmercury cathode and electrolyte; electrical connections to said flowingmercury cathode; an anode assembly serving as cell cover, said anodeassembly comprising graphite blocks disposed parallel to each other withtheir longitudinal axes at right angles to the longitudinal axis of thecell, narrow gaps between adjacent blocks for the removal of chlorinetherethrough and concrete hoods in gas-tight relation to adjoiningblocks forming an enclosed space above each of said gaps for receivingthe chlorine, said graphite blocks being supported above the cathode bymeans of hard rubber strips resting on the bottom of the trough and soarranged that substantially the whole of the under surface of saidgraphite blocks is in contact with the electrolyte, the exterior surface'of said graphite blocks opposite to said under surface being coatedwith a chlorine fed to the cell, the velocity of the brine in theelectro* lysis gap is increased several times. in any case, it isincreased sufficiently to sweep away the chlorine bubbles fromtheunder-surface of the anode. The sweeping away of the bubbles effectsa considerable reduction in the voltage drop across the electrolysisgap. This permits operation of the electrolytic cell at a lower voltagewith the same current, or at a higher current with the same voltage.

4. With the entire quantity of brine in the electrolysis gap, theconcentration of the brine throughout the cell is more uniformpermitting operation at a lower voltage.

5. With the brine velocity equal to or greater than that of the mercury,the debris is more readily removed impervious composition, said exteriorsurface of each of said graphite blocks having a shallow groove alongits length for receiving electrical conducting means; metallicconductors for supplying electric current enclosed in said grooves,sealed and protected against corrosion.

2. An electrolytic cell comprising an elognated trough of U-shaped crosssection, inclined in a longitudinal direction to provide for the flow ofmercury cathode and electrolyte; electrical connections to said flowingmercury cathode; an anode assembly serving as cell cover, said anodeassembly comprising graphite blocks disposed parallel to each otheracross the cell, narrow gaps between adjacent blocks for the removal ofchlorine therethrough and chlorine receiving hoods along each of saidgaps forming an enclosed space thereabove, said hoods being maintainedin gas-tight relationship with adjoining blocks by means of a chlorineimpervious composition applied along the edges of contact with theblocks, said blocks being supported above the cathode by means ofspacers resting on the bottom of said trough and so arranged thatsubstantially the Whole of the under surface of said blocks is incontact with the electrolyte, the exterior surface of said blocksopposite to said under surface being coated With a chlorine imperviouscomposition; and means for conducting electricity to individual anodeblocks.

3. An electrolytic cell comprising an elongated trough of U-shaped crosssection, inclined in a longitudinal direction to provide for the flow ofmercury cathode and electrolyte; electrical connections to said flowingmercury cathode; an anode assembly serving as cell cover, said anodeassembly comprising graphite blocks disposed parallel to each other withtheir longitudinal axes at right angles to the longitudinal axis of thecell, narrow gaps between adjacent blocks for the removal of chlorinetheretlu'ough and hoods extending the full length of each gap forming anenclosed space thereabove, said hoods being maintained in gas-tightrelationship with adjoining blocks by means of a chlorine imperviouscomposition applied along the edges of contact with the blocks, saidblocks being supported above the cathode by means of spacers resting onthe bottom of said trough and so arranged that substantially the wholeof the under surface of said blocks is in contact with the electrolyte,the exterior surface of said graphite blocks opposite to said undersurface being coated with a chlorine impervious composition; and meansfor conducting electricity to individual anode blocks.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES FIAT Report No. 816, P. B. 33,221, May 15, 1946. HorizontalMercury Chlorine Cell, pages 21 and 22. Publication of the. Office ofTechnical Services.

1. AN ELECTROLYTIC CELL COMPRISING AN ELONGATED TROUGH OF U-SHAPED CROSSSECTION, INCLINED IN A LONGITUDINAL DIRECTION TO PROVIDE FOR THE FLOW OFMERCURY CATHODE AND ELECTROLYTE; ELECTRICAL CONNECTIONS TO SAID FLOWINGMERCURY CATHODE; AN ANODE ASSEMBLY SERVING AS CELL COVER, SAID ANODEASSEMBLY COMPRISING GRAPHITE BLOCKS DISPOSED PARALLEL TO EACH OTHER WITHTHEIR LONGITUDINAL AXES AT RIGHT ANGLES TO THE LONGITUDINAL AXIS OF THECELL NARROW GAPS BETWEEN ADJACENT BLOCKS FOR THE REMOVAL OF CHLORINETHERETHROUGH AND CONCRETE HOODS IN GAS-TIGHT RELATION TO ADJOININGBLOCKS FORMING AN ENCLOSED SPACE ABOVE EACH OF SAID GAPS FOR RECEIVINGTHE CHLORINE, SAID GRAPHITE BLOCKS BEING SUPPORTED ABOVE THE CATHODE BYMEANS OF HARD RUBBER STRIPS RESTING ON THE BOTTOM OF THE TROUGH AND SOARRANGED THAT SUBSTANTIALLY THE WHOLE OF THE UNDER SURFACE OF SAIDGRAPHITE BLOCKS IS IN CONTACT WITH THE ELECTROLYTE, THE EXTERIOR SURFACEOF SAID GRAPHITE BLOCKS OPPOSITE TO SAID UNDER SURFACE BEING COATED WITHA CHLORINE IMPERVIOUS COMPOSITION, SAID EXTERIOR SURFACE OF EACH OF SAIDGRAPHITE BLOCKS HAVING A SHALLOW GROOVE ALONG ITS LENGTH FOR RECEIVINGELECTRICAL CONDUCTING MEANS; METALLIC CONDUCTORS FOR SUPPLYING ELECTRICCURRENT ENCLOSED IN SAID GROOVES, SEALED AND PROTECTED AGAINSTCORROSION.